Vinyl acetate-containing compositions for splicing sheet materials



3,322,714 VINYL ACETATE-CONTAINING COMPOSITIONS FOR SPLICING SHEETMATERIALS Wilhelm N. Martin, GrandMcre, Quebec, Canada, as-

signor to Consolidated Paper (Bahamas) Limited, Nassau, Bahamas NoDrawing. Filed Aug. 31, 1964, Ser. No. 393,352

6 Claims. (Cl. 26031.8)

This invention relates to a process for preparing polyvinyl acetateresin compositions and to heat hardenable adhesive films preparedtherefrom, such films when cured, being heat resistant and, if desired,water dispersible. These films are useful in the splicing of the lappedends of paper webs and the like.

It has heretofore been proposed to produce a heat hardenable polyvinylacetate film using an unmodified polyvinyl acetate resin and a metalhalide as a curing agent. A disadvantage of such a film is that, whenemployed to form a splice, the film or splice becomes sufiicientlydiscolored to make it highly objectionable to those who require asubstantially undetectable splice. Furthermore, this film is not waterdispersible. Moreover, the use of some metal halides as curing agentsresults in excessively long curing periods, while still others tend togel the resin solution very rapidly at room temperature.

Properties of heat resistance and water dispersibility are becomingincreasingly important wherever these splicing films are used in thepaper and printing industries. Printing processes involving a relativelyhigh temperature ink drying step, require that the paper splices be suchthat they will withstand these drying temperatures. The repulping ofused or unused paper for re-use in the paper making process requiresthat the paper splice be water dispersible so as to simplify thereclamation process.

An object of the present invention is to provide a heat hardenablepolyvinyl acetate splicing composition which when cured possessesimproved heat resistant properties and which is not subject todiscoloration.

Another object is to provide a heat hardenable polyvinyl acetatesplicing film which when cured is highly heat resistant and waterdispersible.

Another object is to provide a process for preparing heat hardenablepolyvinyl acetate splicing films which when cured are heat resistant andwhich may be also water dispersible.

In accordance with the invention a modified polyvinyl acetate isdissolved in a suitable organic solvent such as methanol, ethanol,methyl ethyl ketone, benzene, ethyl acetate. Preferably, this modifiedpolyvinyl acetate resin is of carboxylated type. Suitable commerciallyavailable carboxylated polyvinyl acetate resins are those known underthe trade name Gelva C-3 and Gelva C-5 of Monsanto Chemical Company.These are copolymers of vinyl acetate and crotonic acid. They aremodified vinyl acetate resins which have been carbonized to such degreethat they can be dissolved or dispersed in alkali solutions. Theseresins have viscosities in the range of 9 to 33 centipoises. Thepreferred solvents are the lower alcohols such-as methanol and ethanol.

A curing agent containing a multivalent metal, and.

preferably a compound in which the anion is associated with a weak acid,is employed. The curing agent may be dissolved in the modified polyvinylacetate solution in an amount equal to 2 to 10% by weight of thepolyvinyl acetate.

Examples of suitable curing agents are aluminum acetate, aluminumnitrate, aluminum sulphate, ammonium bichromate, chromium acetate,chromium chloride, chromium nitrate, chromium trioxide, ferric oxalate,ferric chloride, and ferric citrate. Chromium acetate is the preferredcuring agent.

A plasticizer is added to the solution. The plasticizer 3,322,7MPatented May 30, 1967 may be of the usual type and may be selected fromthe group comprising dibutyl phthalate; a polyglycol such aspolyethylene glycol di(2-ethylhexoate), methoxypolyethylene glycol, andtriethylene glycol di(2-ethylbutyrate); also butyl phthalyl, butylglycolate; butyl ricinoleate; and glyceryl triacetate.

The resulting casting solution has a preferred concentration in therange of 15-50% by weight of total nonvolatile material.

For the production of a film, the resulting solution is cast upon asmooth surface as a thin layer which, on drying, results in a film whichmay be readily peeled off the surface. The solvent is evaporated at atemperature of the order of 250 F. (or lower) to leave the dried film.

The film, produced as described and used as hereinafter described, isheat resistant to a temperature of the order of 400 F.

The water dispersibility of the film may be increased to any desireddegree by adding to the solution sodium hydroxide in an amount of 2 to10% by weight of the modified polyvinyl acetate. Additions of NaOHbeyond 10% renders the resulting film susceptible to conditions of highhumidity, under which conditions the film will soften and becomedifiicult to handle.

In some cases, the film may be cast directly upon a paper surface, whichhas been coated or treated to give a smooth surface from which the filmmay be freely peeled after it has dried. Thus, after drying, the filmmay be peeled from the casting surface, packaged with an interleavinglayer of paper (preferably repulpable), cut into desired shapes andsizes, placed in any additional packaging means, and marketed. After thefilm has been peeled off from the coated or treated paper, this papermay be re-wound for re-use in further coating operations; alternatively,this coated or treated paper may be used directly in the packaging ofthe film as the interleaving material. Examples of such a castingsurface are polyethylene coated kraft paper, silicone treated paper andKVP paper (emulsified bleached parch-kraft paper).

In other cases, the film may be cast directly upon a smooth, flexible,travelling, endless belt, from which it may be peeled after it has driedand packaged in a manner similar to that described above. Such anendless belt:

may be made of metal or plastic.

When using the film in a splicing operation, it is peeled from itspackaging surface, placed as an interlayer between the two surfaces tothe adhesively secured or spliced together, and heated to a curingtemperature of about 325475 F. under slight pressure for suflicient timefor the bonding action to take place, For instance, the heat andpressure may be applied by means of a hand iron.

It will be appreciated that the casting solution as described may besupplied directly to the user who may employ it to produce the splicingfilm in situ. In some instances, it may be desirable to supply thecuring agent in a separate container for addition to the solution justbefore use.

The following examples are illustrative of the invention:

Example I A solution containing the following ingredients was preparedat room temperature:

Parts by wt. (dry solids) The above solution was cast on a polyethylenecoated kraft paper and dried under heat lamps at a temperature in theorder of 250 F. to a film thickness of 1.0 mil: The film was foundeffective in splicing such materials 4 The following test procedure wasemployed to measure heat resistance.

Two strip heater (250 watts, known under the trade name Chromalox) wereset approximately 1 inch apart;

as newsprint, kraft paper, glossy or heavily filled and 5 the heaterswere connected to an auto-transformer, for coated papers, aluminum foil,etc. Splices were made at temperature control; two strips of paper (1"wide) which an ironing temperature of between 375425 F. Even had beenspliced together (as hereinafter described) by if ironing was prolongedthere was little or no discoloraa 4; high x 1 wide piece of the splicingfilm to be tested tion of the splice. When the heat resistance of thesplice were suspended such that one strip was held from above was testedby the test procedure described later, the 9 so that the splice wascentered between the two strip splice did not fail, in fact, the paperbegan to char while heaters and the other strip was pulled from below bythe splice was still intact. a 1 kg. weight attached to it; athermometer placed close If an unmodified polyvinyl acetate resin issubstituted to the splice indicated the temperature condition; the forthe above carboxylated resin, in Example I, the heat temperature betweenthe heaters in the region of the splice resistance of a splice made withthe resulting film will be was approximately 400 F., the time for thesplice to much lower. If, however, chromium chloride is also subyield(i.e. for the weight to drop) was measured with a stituted for thechromium acetate, while the heat resiststop watch. The term slight heatresistance in above ance of the splice will be increased, the splicewill become table covers a range of a few seconds to approximatelydiscolored. Similarly, if the chromium acetate is left out seconds; theterm good indicates a heat resistance of the above formulation (ExampleI) the heat resistance 20 of over 60 seconds. of the splice will also bemuch lower; it will, however, I claim: be water dispersible in aqueoussolutions which are 1. A composition for splicing sheet material whichmildly alkaline. consists essentially of a solution of a copolymer ofvinyl Example 11 acetate and crotonic acid, a plasticizer, and a curingParts bywt (dry solids) agent selected from the group consisting ofaluminum carboxylated polyvinyl acetate (Gelva acetate, aluminumnitrate, aluminum sulphate, ammo- 20) g 12 mum hichrornate, chromiumacetate, chromium chloride, Dibutyl phthalate 12 chromium nitrate, chromum trioxide, ferric oxalate, fer- Ch-mmium acetate (added, for example,in the form ric chloride, and ferric citrate, said composition containofa 30% (weight/volume) aqueous solumg 15% to total nopivolatllematenrfll' tion) g 0.21 2. composition for splicing sheet material asdefined Sodium hydroxide (added, for example, in the in claim 1, whereinthe solvent in said solution 18 selected form of a 16% (Weight/Volume)aqueous So1u from the group consisting of methanol and ethanol. tion)039 3. A composition for sphcmgsheet material as defined Methanol 23 inclaim 1, wherein said plasticizer is dibutyl phthalate. Water(additional to (l) and (2)) 1 2 4. A composition for splicing sheetmaterial as defined The heat resistance of a splice made with this filmon in claim f z l i l l l i d ptesent m an paper is over 400 F. If thechromium acetate is left out, g O y i 0 2 i t 1 a film will result whichwill be water dispersible but will mg ea f. s 6 ma f l be heat resistantonly to about 250 F. for prolonged splclng m comprises .ormmg acomposmon periods consisting essentially of a solution of a copolymer ofabove Solution was cast on a polyethylene Coated vinyl acetate and.CIOtOI'llC acid in a solvent selected from kraft paper surfaceand thefilm dried and tested. The the group conslstmg of methanol l methy1ethyl results were similar to that indicated under Example I, ketone,benzene and ethyl t a agellt except that in addition the film was waterdispersible to amount of 2% to 10% by Welght of said r651", Baldahi-gh'degre'e, curing agent being selected from the group consistingTable I shows results using various curing agents while of aluminumacetate, aluminum aluminum employing the other ingredients and the sameproporp ammonium bichromate, chromium acetate. h tions set forth inExample I. mium chloride, chromium nitrate, chromium trioxide,

TABLE I Splice Compound Amolllllll. used, Heag;tl;t0e0s isltanceDiscoloration Aluminum Acetate Aluminum Nitrate Chromium Acetate. Verysli ht. Chromium Chloride. Yellowrown. Chromium Nitrate Sliglg.

o. Chromium Trioxide Liglg brown.

Ferric Nitrate Ferric Oxalate. Slight. Ferric Chloride. Veryb dark.

Ferric Citrate V o. Slight.

ferric oxalate, ferric chloride, and ferric citrate, and a plasticizer,said composition containing a total of 15% to 50% non-volatile material,casting said composition as a thin layer on a smooth surface, allowingsaid layer to dry, and peeling the dried layer from said surface.

6. A method of making a heat resistant sheet material splicing film asdefined in claim 5, wherein said smooth surface comprises the surface ofa plastic composition coating on a paper sheet.

References Cited UNITED STATES PATENTS 2,424,110 7/1947 Morrison et al.260-33.4 3,092,600 6/1963 Ozawa et al 260-85] 3,100,775 8/1963 Ehrlich260-334 MORRIS LIEBMAN, Primary Examiner. L. T. JACOBS, AssistantExaminer.

1. A COMPOSITION FOR SPLICING SHEET MATERIAL WHICH CONSISTS ESSENTIALLYOF A SOLUTION OF A COPOLYMER OF VINYL ACETATE AND CROTONIC ACID, APLASTICIZER, AND A CURING AGENT SELECTED FROM THE GROUP CONSISTING OFALUMINUM ACETATE, ALUMINUM NITRATE, ALUMINUM SULPHATE AMMONIUMBICHROMATE, CHROMIUM ACETATE, CHROMIUM CHLORIDE CHROMIUM NITRATE,CHROMIUM TRIOXIDE, FERRIC OXALATE, DERRIC CHLORIDE, AND FERRIC CITRATE,SAID COMPOSITION CONTAINING 15% TO 50% TOTAL NON-VOLATILE MATERIAL.